In recent years, there has been demand to reduce greenhouse gasses from a perspective of preventing global warming. Regarding refrigerants used for refrigeration cycle apparatus such as air-conditioning apparatus, those with a lower global warming potential (GWP) are being considered. The GWP of R410A widely used for air-conditioning apparatus at present is as high as 2088. Difluoromethane (R32) that has begun to be introduced recently has a considerably high GWP value of 675.
Examples of refrigerant with a low GWP include carbon dioxide (R744: GWP=1), ammonia (R717: GWP=0), propane (R290: GWP=6), 2,3,3,3-tetrafluoropropene (R1234yf: GWP=4), and 1,3,3,3-tetrafluoropropene (R1234ze: GWP=6).
These low-GWP refrigerants are difficult to apply to typical air-conditioning apparatus because of the following problems.                R744: There is a problem in securing withstanding pressure because of very high operating pressure. Also, because critical temperature is as low as 31 degrees C., there is a problem of how to secure performance in application to air-conditioning apparatus.        R717: Because of high toxicity, there is a problem in ensuring safety.        R290: Because of high flammability, there is a problem in ensuring safety.        R1234yf/R1234ze: Because a volume flow rate increases at low operating pressure, there is a problem of performance deterioration due to increases in pressure loss.        
A refrigerant capable of solving the above problems is 1,1,2-trifluoroethylene (HFO-1123) (see, for example, Patent Literature 1). The refrigerant has the following advantages, in particular.                Because of its high operating pressure and low volume flow rate, the refrigerant involves a reduced pressure loss and can readily ensure performance.        The refrigerant has a GWP of less than 1 and has an edge in countermeasures against global warming.        